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Abstract:

A spray nozzle 10 for a laser deposition apparatus comprises an array of
nozzle apertures 16 arranged side-by-side, and a powder supply chamber 18
in fluid communication with the nozzle apertures 16. In use the powder
supply chamber 18 supplies powder to the nozzle apertures 16 under
pressure so as to cause a wide powder stream to be discharged from the
array of nozzle apertures 16. When used with a laser deposition apparatus
100, a relatively wide coating of a uniform thickness can be deposited.

Claims:

1. A spray nozzle for a laser deposition apparatus, comprising: an array
of nozzle apertures arranged side-by-side; and a powder supply chamber in
fluid communication with the nozzle apertures and arranged in use to
supply powder to the nozzle apertures under pressure so as to cause a
wide powder sheet to be ejected from the array of nozzle apertures.

2. A spray nozzle according to claim 1, wherein the array of nozzle
apertures is a linear array.

3. A spray nozzle according to claim 1, wherein the nozzle apertures are
of differing sizes.

4. A spray nozzle according to claim 3, wherein the nozzle apertures
towards the edges of the array are larger than the nozzle apertures
towards the middle of the array.

5. A spray nozzle according to claim 1, wherein at least one nozzle
aperture within the array is provided with a flow regulator for
regulating the flow of powder through the said nozzle.

6. A spray nozzle according to claim 5, wherein each nozzle aperture
within the array is provided with an individual flow regulator for
regulating the flow of powder through it.

7. A spray nozzle according to claim 1, further comprising upper and
lower elongate gas apertures located above and below the array of nozzle
apertures respectively and extending substantially parallel to the array
of nozzle apertures, wherein the upper and lower elongate apertures are
arranged to eject a wide gas stream above and below the wide powder
sheet.

8. A spray nozzle according to claim 1, further comprising upper and
lower guide plates located above and below the array of nozzle apertures
respectively and extending so as to guide the flow of powder ejected from
the spray nozzle in use.

9. A spray nozzle according to claim 1, wherein a wall of the powder
supply chamber is provided with ribs which extend generally in the
direction of flow through the powder supply chamber in use.

10. A spray nozzle according to claim 1, wherein the array of nozzle
apertures is formed in a nozzle body.

11. A laser deposition apparatus comprising a laser arranged to generate
a wide laser beam and a spray nozzle in accordance with claim 1.

Description:

[0001] The present invention relates to a spray nozzle for a laser
deposition apparatus.

[0002] Laser cladding is a technique that is generally used either to
deposit a coating onto a component in order to rebuild the component, or
to deposit a coating onto a substrate in order to provide a protective
layer.

[0003] A laser cladding apparatus typically comprises a laser which forms
a molten pool on a substrate into which a stream of metal powder
entrained in a gas can be blown. This results in a track (otherwise known
as a clad) being deposited on the substrate. U.S. Pat. No. 6,316,744
discloses a laser cladding apparatus in which the metal powder is
delivered coaxially with, and around, the laser beam.

[0004] The intensity of the laser beam usually has a Gaussian distribution
which means that the centre of the melt pool is at a significantly higher
temperature than the temperature of the surrounding areas. If it is
necessary to deposit a relatively wide coating then this must be done by
overlapping a series of clads side-by-side. If only the laser beam
diameter is increased then the temperature at the centre of the melt pool
is such that high levels of vaporisation of additive material may occur,
or the substrate may melt to an excessive depth. Further, the surrounding
substrate material may be disrupted to an excessive depth and the
deposited coating may dilute into the substrate. In some application
dilution of the clad by the parent substrate may occur. If a number of
clads are overlapped side-by-side then the reworking of previously
deposited clads can induce unwanted material properties. Further,
cavities may form between adjacent clads which is undesirable, and the
surface formed may be uneven.

[0005] It is therefore desirable to provide a spray nozzle for laser
deposition and a laser deposition apparatus capable of depositing wide
coating layers of a substantially uniform thickness.

[0006] According to a first aspect of the present invention there is
provided a spray nozzle for a laser deposition apparatus, comprising: an
array of nozzle apertures arranged side-by-side; and a powder supply
chamber in fluid communication with the nozzle apertures and arranged in
use to supply powder to the nozzle apertures under pressure so as to
cause a wide powder sheet to be ejected from the array of nozzle
apertures.

[0007] Preferably the array of nozzle apertures is a linear array. The
nozzle apertures may be of differing sizes. The nozzle apertures towards
the edges of the array may be larger than the nozzle apertures towards
the middle of the array. There may be some applications where it is
desirable to have larger nozzle apertures towards the centre or towards a
side of the array. Larger apertures towards a side of the array may help
the formation of radial tracks, for example hard-facing of gate valves.

[0008] At least one nozzle aperture within the array may be provided with
a flow regulator for regulating the flow of powder through the said
nozzle. In a preferred arrangement each nozzle aperture within the array
is provided with an individual flow regulator for regulating the flow of
powder through it.

[0009] The spray nozzle may further comprise upper and lower elongate gas
apertures located above and below the array of nozzle apertures
respectively that extend substantially parallel to the array of nozzle
apertures, wherein the upper and lower elongate apertures are arranged to
eject a wide gas stream above and below the wide powder sheet.

[0010] The spray nozzle may further comprise upper and lower guide plates
located above and below the array of nozzle apertures respectively that
extend so as to guide the flow of powder ejected from the spray nozzle in
use.

[0011] A wall of the powder supply chamber may be provided with ribs which
extend generally in the direction of flow through the powder supply
chamber in use. These ribs would help to guide the flow. Alternatively or
in addition, the powder supply chamber may be provided with baffles which
extend generally in a direction perpendicular to the direction of flow
through the powder supply chamber in use. Such baffles would help to
promote turbulence in the supply chamber.

[0012] Preferably the array of nozzle apertures is formed in a nozzle
body, i.e. a single integral unit.

[0013] The invention also concerns a laser deposition apparatus comprising
a laser arranged to generate a wide laser beam and a spray nozzle in
accordance with any statement herein.

[0014] The invention may comprise any combination of the features and/or
limitations referred to herein, except combinations of such features as
are mutually exclusive.

[0015] Embodiments of the present invention will now be described, by way
of example only, with reference to the accompanying drawings, in which:

[0016]FIG. 1 schematically shows a spray nozzle according to a first
embodiment;

[0024]FIG. 9 schematically shows a cross-sectional view of a spray nozzle
according to a third embodiment;

[0025]FIG. 10 schematically shows an end view of the spray nozzle of FIG.
9; and

[0026]FIG. 11 schematically shows a cross-sectional view of a spray
nozzle according to a fourth embodiment.

[0027] FIGS. 1 and 2 show a spray nozzle 10 comprising a chamber body 12,
a nozzle body 14 and a supply duct 20. An array of nozzle apertures 16 is
provided in the end of the nozzle body 16. The array of nozzle apertures
comprises a plurality of individual nozzle apertures 16 arranged
side-by-side. The nozzle apertures 16 extend through the nozzle body 14
and lead to a powder supply chamber 18 which is formed by the chamber
body 12. The chamber body 12 has end walls 11, 13 that abut the nozzle
body 14 and the supply duct 20 respectively. As can be seen from the
sectional view A-A, the powder supply chamber 18 has cross-sectional area
that tapers towards the array of nozzle apertures and is in fluid
communication with the supply duct 20. However, in other embodiments the
powder supply chamber 18 may have a substantially constant
cross-sectional area. The nozzle apertures 16 are arranged in series and
the centres of the nozzle apertures 16 lie on a straight line. In other
embodiments the nozzle apertures 16 may be arranged in a different
geometry. The nozzle body 14, the chamber body 12 and the supply duct 20
may be formed from separate components welded together. Alternatively,
they may be integrally formed with one another.

[0028] In use, metal powder is supplied to the spray nozzle 10 via the
supply duct 20 under pressure using a carrier gas. The metal powder and
carrier gas mix in the powder supply chamber 18, which acts as a plenum
chamber, and the powder exits the array of nozzle apertures 16 as a wide
sheet (or stream) of powder.

[0029] As shown in FIG. 3 the powder supply chamber 18 may be provided
with longitudinally extending ribs 19. The ribs 19 help to ensure laminar
flow and also act to stiffen the spray nozzle 10. However, transverse
baffles 19a may be provided in addition or instead in order to produce a
turbulent flow.

[0030] With reference to FIG. 4, the spray nozzle 10 may be used with a
laser cladding apparatus 100 which is arranged to deposit a coating 3
onto the surface 2 of a substrate 1. In addition to the spray nozzle 10,
the laser cladding apparatus 100 comprises a laser 102 capable of
generating a wide laser beam 104, means for moving the substrate 1 and a
powder feeder (not shown) for feeding a metal powder to the nozzle 10 via
the supply duct 20. As the substrate 1 is moved in direction X, the
nozzle 10 emits a sheet (or stream) of powder 4 which interacts with the
laser beam 104. As the powder sheet 4 meets the laser beam 104 it is
melted to form a melt pool on the substrate surface 2, which solidifies
as a coating 3 on the surface 2. The width of the laser beam 104 is
comparable to that of the powder sheet 4 which ensures that the whole
width of the powder sheet 4 is melted and deposited as a coating 3. The
wide laser beam 104 may be generated by any of the following beam
manipulation techniques: scanning, diode, refractive, diffractive,
ancillary, array. Multiple laser beams could also be used side-by-side in
order to generate a wide laser beam, Other techniques for generating a
wide laser beam will be readily apparent to one skilled in the art.

[0031] The metal powder may be of a uniform composition or may be a
mixture of two or more powders. The carrier gas may be an inert gas such
as argon, for example. Within the powder supply chamber 18 the metal
powder and carrier gas mix in order to ensure that the powder sheet 4
delivered by the nozzle apertures 16 is uniform in both composition and
delivery rate.

[0032] As shown in FIG. 5a, the laser cladding apparatus 100 described
above can deposit a wide coating 3 of a substantially uniform thickness.
The width of the coating 3 is approximately the same as the width of the
array of nozzle apertures 16. The edges of the coating are substantially
perpendicular to the substrate surface 2. This allows another coating
layer to be deposited next to it without requiring an overlap and
therefore results in a coating having a substantially flat surface. This
improves the mechanical properties of the cladding 3 and reduces the
overall amount of material used when compared with a conventional
apparatus that deposits a number of narrow, domed, coating layers
side-by-side and overlapping.

[0033] Further, a flat deposition can be provided by overlapping clads and
tailoring the thickness of the clads at the edge of each clad. For
example, as shown in FIG. 5b overlapping clad tracks 3 having angled
edges results in a flat deposition layer.

[0034] The powder flow from the spray nozzle can be regulated in order to
alter the mass flow distribution of the powder according to the clad
width and/or thickness required. The powder flow can be controlled and
regulated from the primary powder feed system.

[0035] The array of nozzles apertures 16 can be altered to produce a clad
of a desired geometry. Specifically, the number, size and relative
positions of nozzle apertures 16 can be configured so as to produce a
clad of a desired shape.

[0036] FIGS. 6 and 7 show a second embodiment of a spray nozzle 10 which
can be used with the laser cladding apparatus of FIG. 4. This is similar
to the embodiment of FIGS. 1-3 except the chamber body 12 and the nozzle
body 14 are both tapered towards the nozzle apertures 16. As can be seen
from the cross-sectional view B-B, the powder supply chamber 18 tapers
towards the nozzle apertures 16.

[0037]FIG. 8 shows a variation of the second embodiment in which the
chamber body 12 and the nozzle body 14 are integrally formed.

[0038] FIGS. 9 and 10 show a third embodiment of a spray nozzle 10 which
can be used with the laser cladding apparatus 10 of FIG. 4. An array of
nozzle apertures 16 are formed in the nozzle body 14 and are arranged
side-by-side in a line with the centre of the apertures 16 all lying on
the same line. The plurality of nozzle apertures 16 that constitute the
array are of varying sizes. Specifically, the nozzle aperture 16 at each
end of the array is the largest and the nozzle apertures gradually
decrease in size towards the middle of the array. Each of the nozzle
apertures 16 is provided with an individual flow regulator in the form of
a valve 21. The valve 21 can be controlled to alter the flow rate through
the specific nozzle 16.

[0039] Upper and lower outer walls 15, 17 are spaced from the chamber body
12 and the nozzle body 14 and define upper and lower fluid ducts 22, 24
between the walls 15, 17 and the chamber/nozzle body 12, 14. The upper
and lower fluid ducts 22, 24 have upper and lower inlets 30, 32
respectively for introducing a gas into the ducts 22, 24. The upper and
lower outer walls 15, 17 also define an upper elongate gas aperture 26
above the array of nozzle apertures 16 and a lower elongate gas aperture
28 below the array of nozzle apertures 16. The upper and lower elongate
gas apertures 26, 28 are parallel to the array of nozzle apertures 16.
When a gas is supplied to the ducts 22, 24 via the inlets 30, 32 the gas
is discharged from the upper and lower elongate gas apertures 26, 28 as
sheets. A chamber body 12 is provided which defines a powder supply
chamber 18. The chamber body 12 is attached to the nozzle body 14 such
that the powder supply chamber 18 is in fluid communication with the
plurality of nozzle apertures 16. As in the embodiments of FIGS. 1-3 and
6-8, a supply duct 20 is attached to the chamber body 12 and in use
delivers a powder to the powder chamber 18 so as to eject a wide powder
sheet from the array of nozzle apertures 16.

[0040] Although the walls 15, 17 are shown in FIGS. 9 and 10 as being
integral with the chamber body 12, they could form part of a separate
fairing mounted over the chamber body 12. Such a fairing may be
displaceable on the chamber body 12 and may terminate short of the end
face of the chamber body 12 at which the nozzle body 14 emerges.

[0041] Upper and lower guide plates 34, 36 are attached to the outer walls
15, 17 and project away from the walls 15, 17 and nozzle body 14 in a
direction substantially perpendicular to the end faces. It may be
possible to vary the angle of the guide plates with respect to the nozzle
body 14. The upper guide plate 34 is positioned just above the upper
elongate gas aperture 26 and the lower guide plate 36 is positioned just
below the lower elongate gas aperture 28. As can be seen from FIG. 9, the
upper guide plate 34 is longer than, and therefore projects beyond, the
lower guide plate 36.

[0042] The spray nozzle 10 can be used with the laser cladding apparatus
100 of FIG. 4 to deposit a coating 3 on the surface 2 of a substrate 1.
In use, metal powder is fed to the powder supply chamber 18 through the
supply duct 20 using a carrier gas. A carrier gas is also supplied to the
upper and lower fluid ducts 22, 24 through the inlets 30, 32. The metal
powder is mixed in the powder supply chamber 18 and is caused to exit the
array of nozzle apertures 16 as a wide sheet of powder. The carrier gas
exits the upper and lower elongate gas apertures 26, 28 as wide streams
of gas sandwiching the powder sheet. The Coand{hacek over (a)} effect
causes the streams of carrier gas to be attracted to the powder sheet
ejected from the array of nozzle apertures 16 and helps to ensure that
the powder is ejected from the array of nozzle apertures 16 as a sheet,
the gas-entrained powder issuing as an uninterrupted lamellar flow. This
ensures that a coating of an even thickness is deposited on the substrate
and helps to prevent the powder sheet from diverging. Consequently the
powder coating is improved, because the bulk of the powder lands in the
melt pool on the substrate surface 2, without excess overspray.

[0043] The spray nozzle 10 can deposit a focussed powder sheet (or stream)
which does not diverge to the same extent as powder ejected from
conventional nozzles. This means that the spray nozzle 10 can be located
further away from the surface of the substrate which the coating is to be
deposited on, without reducing the uniformity of the coating layer
deposited.

[0044] The guide plates 34, 36 help to guide the powder and the carrier
gas. Since the upper guide plate 34 is longer than the lower guide plate
36 the spray nozzle 10 can be used at an angle relative to the substrate
surface whilst ensuring that the guide plates 34, 36 fulfil their
function of guiding the powder and the carrier gas.

[0045] The composition of the carrier gas that exits the elongate gas
apertures 26, 28 may be the same as the composition of the carrier gas
used to deliver the metal powder; this may help to avoid mixing of gases.
The carrier gas exiting the elongate gas apertures 26, 28 may exit at a
different velocity from the powder sheet exiting the array of nozzle
apertures 16. Further, the carrier gas exiting the elongate gas apertures
26, 28 may be at a higher temperature than that of the powder sheet so
that the gas pre-heats the powder sheet before it interacts with the
laser beam 104.

[0046] The individual valves 21 can regulate the flow through the
individual nozzle apertures. This is particularly useful if the spray
nozzle 10 is performing a relatively tight arc in the plane of the
substrate surface. The nozzle apertures 16 towards the radially inner
side of the arc, which are travelling relatively slowly, are choked to
reduce the flow rate of powder exiting the nozzle apertures when compared
to the flow rate of powder exiting the nozzle apertures on the radially
outer side of the arc, which are travelling relatively fast. This helps
to ensure that the thickness of the coating is substantially even.

[0047]FIG. 11 shows a further embodiment which is similar to that of
FIGS. 9 and 10 except the guide plates 34, 36 are pivotable with respect
to the nozzle body 14 and the outer walls 15, 17. This allows the powder
and gas streams to be directed. In an alternative arrangement the guide
plates 34, 36 are capable of moving forwards and backwards with respect
to the direction of flow of the powder stream issuing from the array of
nozzle apertures 16.

[0048] In some embodiments it may be possible to tilt or twist the spray
nozzle 10 about a central axis located along the length of the spray
nozzle 16. This has the effect of reducing the width of the coating
deposited whilst maintaining a uniform thickness.

[0049] The spray nozzle 10 may be cooled by either the carrier gas exiting
the elongate gas apertures 26, 28 or by a closed cooling system such as a
water jacket.

[0050] It may be desirable to use two or more spray nozzles 10 with the
laser cladding apparatus 100. For example, two nozzles 10 may be arranged
side-by-side, on top of one another, or positioned either side of the
laser beam 104 but directed towards the same target.

[0052] Although it has been described that the spray nozzle 10 is for use
with a laser cladding apparatus 100, as will be readily apparent to one
skilled in the art, the spray nozzle 10 may be used with other types of
laser deposition apparatus such as laser welding, brazing or soldering.